Any time you have a question that has two different objects with different prices/rates/density/etc., you'll always end up setting up a system of equations. You must have as many equations as there are variables. For instance, you have Coffee A and Coffee B, so two variables, which means two equations.
Now that you know you need two equations, what kind of equations will they be? This is based off of the total amount of each. Since there is a total weight and total cost, you will have one equation dealing with weight and the other dealing with cost. Here, I'll be using A to represent Coffee A, and B representing Coffee B.
since Coffee A costs $5.50 and Coffee B costs $4.30, and both of them added up with their respective amount costs $756.30. Next, look at the weight equation.
since weight is constant no matter what you're measuring, we use a coefficient of just 1 to represent that there is equal weight per unit of each coffee. Use systems of equations from here to determine the amount of each coffee that Pablo has used. You can do this by using either substitution or elimination to cancel out one of the variables and solve it from there. Combined, the two equations look like
Since I prefer using elimination, I'll set it up using elimination. To do this, I want to cancel out the B variable, so I will multiply the bottom equation by 4.30.
Now subtract both equations to cancel out B.
Here, use Algebra to determine the amount of of Coffee A there is, then plug that back in to either equation you want and use PEMDAS to determine Coffee B.